Heat treatment processes include loading a material, such as a metal, into a furnace and applying heat until the material (i.e., the load) reaches a steady-state temperature. The heat treatment itself starts typically when the material reaches uniform steady-state temperature within a certain tolerance defined by a specific temperature threshold: this condition of the load is defined as steady-state condition. If no treatment procedure is specified and there is no knowledge of the time required for the load to reach the steady-state condition, then conventional heat treatment processes utilize a load thermocouple inserted into the load to determine when the load reaches the steady-state temperature. However, utilizing load thermocouples has several disadvantages, including time delay due to the setup of the sensor and expense due to their replacement when the sensor wears. Knowledge of the time when the load has reached steady-state uniform temperature would allow advancement to the next step of the heat treatment process in the minimum time with consequent savings of time, energy, and costs and increase the throughput and the utilization of the furnace.
Without a load thermocouple and without a predefined procedure, conventional heat treatment processes rely on experience-based and/or indirect techniques of estimating the time required to heat the load to a target temperature. One such technique includes software models based on complex mathematics that rely on data such as emission constants, physical dimensions of the load, and how the load is placed in the furnace. This technique is unreliable when such parameters are not available and is not suitable for implementation on process controllers. Another technique includes a human operator opening the furnace to view the load. This technique requires highly experienced operators and also introduces a temperature loss. Yet another technique includes measuring the active electrical power supplied to the furnace and assessing when it has reached the steady-state condition. But the active power measurement is not always available and this property is indirect in relation to the load temperature. In fact, the power time profile is affected by changes to the size and shape of the load and therefore the relation between load temperature and supplied power is dependent on the particular load. These conventional techniques are unsuitable for implementing a sensor-less identification of the load steady-state condition that is robust against the variation of the load and at the same time a simplified and immediate interface through which the user can set the desired load temperature threshold to be achieved.